Our overall goal is to gain better understanding of the immune response to ovarian carcinoma (OvC) and make possible earlier diagnosis and more effective therapy. Several years ago we constructed an ELISA to detect mesothelin in body fluids and showed that it may aid in the diagnosis of tumors which express this molecule, including OvC, to satisfy a great clinical need. We subsequently found that the molecule shed from tumor cells and detected by the ELISA is mesothelin variant 1. We recently constructed an assay for antibodies to native mesothelin. Preliminary data indicate that the antibodies are most frequent in OvC patients who are temporarily tumor-free following therapy and in younger women with ovarian autoimmunity (oophoritis), and that circulating antibodies and antigen coexist in some patients with advanced disease. Based on these findings, we hypothesize that when antigen concentrations are low (as in early stage disease), free antibodies are in excess and are more readily measured while in the presence of tumors expressing mesothelin, antigen is in excess and is more readily measured. Measuring both antigen and antibodies may aid diagnosis and monitoring of patients with OvC. Furthermore, the relative availability of antibodies and their ability to influence the host response may change during the course of disease and may affect therapeutic strategies, including immunotherapeutic approaches. We also hypothesize that circulating mesothelin, alone and as part of immune complexes, can facilitate the escape of tumors from immunological control by a mechanism that may involve immature APC and Treg cells, and that vaccination against mesothelin can be beneficial. We propose to test these hypotheses under three Specific Aims. First, we will investigate whether the levels of mesothelin and anti-mesothelin antibodies in sera from patients with OvC and women with ovarian autoimmunity correlate with their clinical state to aid diagnosis and prognosis. Second, we will evaluate mesothelin as a target for humoral and cell-mediated host responses to OvC. Third, we will study in egg-laying hens, which spontaneously develop OvC similar to the human counterpart, the relationship between circulating mesothelin and anti-mesothelin antibodies to tumor formation OvC and investigate whether the occurrence of OvC can be delayed or abrogated by vaccination against mesothelin. Our proposed study is based on novel observations, combines expertise in cancer immunology and autoimmunity and comprises studies both with human subjects and in an appropriate animal model. While we focus on OvC, the information obtained should be relevant also for other tumors that overexpress mesothelin, including mesothelioma and pancreatic carcinoma. PUBLIC HEALTH RELEVANCE: Earlier work by our group has demonstrated that most ovarian cancers express mesothelin and led to an assay that complements the previous `gold standard'CA125 to facilitate diagnosis. We have recently constructed an assay to measure antibodies to mesothelin to improve diagnosis. The proposed work aims to evaluate this assay and also to develop immunotherapy targeting mesothelin.